ARC FLASH AND ARC BLAST BASICS AND TUTORIALS

In addition to the hazards of direct electrical shock, the production electrician faces other hazards as well, including arc flash and arc blast. In fact, according the National Fire Protection Association (NFPA), most electrical accidents that require admission to the hospital are caused by arc flash burns, not because of electrical shock.

In the United States alone, over 2000 people are admitted to burn centers with severe burns
due to arc flash each year.

An arc flash is when the air around a conductor becomes ionized and changes from an insulator to a conductor. When that happens, the live conductor can discharge through the air to another live conductor or to a grounded conductor.

The surrounding air can erupt in a plasma ball that engulfs the air and then dissipates in a fraction of a second. The temperature of the air can reach 19,427°C (35,000°F).  If anyone is unfortunate enough to be in the arc flash zone, they could be severely burned.

In addition to the danger of the flash, an arcing conductor can produce an explosive blast with tremendous pressure. In the presence of the ultrahigh temperatures produced by an arc flash, copper can vaporize and expand 67,000 times, producing a shower of molten metal.

The blast can reach thousands of pounds per square foot and cause great damage,including ruptured eardrums, collapsed lungs, concussions, and internal organ ruptures.

The likelihood of an arc flash increases as the voltage increases: the higher the voltage the more likely it could happen. The size of the flash also depends on the voltage — the higher the voltage, the larger the arc flash — as well as the impedance of the circuit feeding it and the available fault current.

An arc can be initiated by several triggers. Dust, impurities, and corrosion of insulators can initiate an arc and cause it to flash over. Water condensation or dripping water can also create a conductive path for an arc to flash over.

Sometimes arcs are caused by a person accidentally touching a live part or dropping a tool into live equipment. Conductors can also flash over if the voltage is high enough and the gap to another conductor or ground is short enough. And sometimes the insulating material breaks down, allowing an arc to jump through it or around it.

NFPA 70E – Standard for Electrical Safety in the Workplace spells out the flash protection boundary within which a person could receive a second degree burn in the event of an arc flash. For under 300 volts, the flash protection boundary is 4 feet, although unqualified personnel are not allowed within 10 feet unless they are escorted by a qualified person.

We can’t predict when an accident like an arc flash will take place, but there are steps we can take to protect ourselves in the event of such an accident. When we’re working around live electrical equipment we can wear protective clothing such as flame-resistant (FR) clothing and V rated gloves (gloves rated and tested for a particular voltage), and use V-rated tools.

We can also wear clothing made with non-melting fabrics, such as cotton, and avoid wearing clothing made with fabric that will melt with excessive heat, such as nylon, polyester, spandex, and other synthetic fabrics.

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